Process for refining fatty compounds



Patented Jan. 6, 1942 PROCESS FOR REFINING FATTY COMPOUNDS Willem Johannes Dominicus van Dijck,

The Hague, Netherlands No Drawing. Application May 20, 1940, Serial No. 336,221. In the Netherlands June 9, 1939 9 Claims.

This invention relates to the removal of undesirable constituents such as free fatty acids, coloring bodies, mucilaginous materials, etc. from oils, fats, waxes and greases of the. ester type whether of natural or synthetic origin. It deals r particularly with an improved countercurrent extraction method of refining such fatty matters whereby products of superior quality may be obtained in a more economical manner.

In order to make the invention more clear it will be described with more particular reference to the refining of animal and vegetable oils with aqueous ammoniacal alcohol. It is to be under.- stood, however, that this is only one illustrative example of the many advantageous applications of the process and that the invention is not limited thereto.

It has been proposed to remove fatty acids from fatty oils by contacting them with aqueous ammoniacal alcohol whereby, on stratification, two liquid layers are formed, namely an oil layer and a solution of ammonia soaps in aqueous alcohol. The alcohol was thus intended to serve as a solvent for the soaps formed by neutralization of the free fatty acid. After separation of the phases it was suggested that the extract be distilled to remove alcohol, water and ammonia from the fatty acid.. The oil layer could then be treated again with a further quantity of ammoniacal alcohol. In practice this proposed procedure was found to involve disadvantages which made it impractical, particularly because *of emulsification difliculties and losses of ester through saponification. Thus in order to be carried out with economically feasible amounts of alcohol the extraction must be conducted.

countercurrently but when such a procedure is used the bulk of the free acid is removed in the first extraction stage in which the fatty oil to be deacidified is treated for the first time. The ammonia required for neutralizing the acid is, however, introduced in the last stage. As a result a large excess of ammonia is present in all of the extraction stages except possibly the first. This constitutes a very serious disadvantage since not only does the excess base lead to saponification of esters with consequent loss of valuable oil but also, for less obvious reasons which will be discussed hereinafter, the tendency to form undesirable emulsions is increased.

salts from esters. Still other objects and advantages of the invention will be apparent to those skilled in the art from the following description.

It has been found that not only the saponification losses but, unexpectedly, also the emulsification difiiculties of the prior methods may be overcome by regulating the addition of base, e. g. ammonia, in such a manner that no detrimental excess is present at any stage of the reaction. Since the tendency to form emulsions would be expected to depend upon the concentration of the soaps formed by neutralization of the free fatty acid it would not be predicted that avoidance of excess of ammonia could reduce emulsification, since in order to obtain an oil meeting the commercial requirement that the free fatty acids be less than 0.1% by weight, the same amount of soap must be produced. in any case. In fact, excess of ammonia might be expected to be advantageous in that it would reduce 'the concentration of the soap. Actually it has been found, however, that if a large excess of base such as ammonium hydroxide is present the time of settling is almost the same regardless of wide differences in concentration of ammonium salts.

Based upon these findings an improved refining procedure has been developed comprising adding the base to be used in neutralizing the free acid in separate portions in different stages of the countercurrent extraction with a suitable solvent for the soap formed. Thus, for example, when adding ammonia the greater part is preferably added in the first stage with the crude oil feed and an additional amount in the-last extraction stage with the fresh solvent feed. If desired a further amount of ammonia may be added in one or more intermediate stages provided no detrimental excess is thereby brought about.

The process of the inventionmay be carried out in any suitable apparatus. A particularly advantageous multi,-stage countercurrent arrangement is described, for example, in United States Patent 2,164,189. Using such a battery of mixers and centrifugal separators extraction according to the invention in at least two and more, preferably about four, stages has been found to give excellent results with a variety of fatty oils. The process may also be carried out in a unitary apparatus such as an extraction column, whether of the packed type or not, into which controlled amounts of the chosen base may be injected at suitable points to give the desired concentration throughout the extraction. A plurality of such columns or other suitable units for contacting immiscible liquids may be used with or without phase separatingmeans therebetween.

The quantity of base which it will be desirable to use in any given case will depend upon the nature of the crude fatty material being refined and the refining agents chosen. The proportion of the total base which should be introduced at any one point in the system will be influenced by the same factors and will also depend somewhat upon the operating conditions adopted. One advantageous procedure is to feed into the first extraction stage a quantity of ammonium hydrox-' ide or anhydrous ammonia stoichiometrically equivalent to the free fatty acid present in the crude fatty matter being fed and a small additional amount, sufiicient to suppress undesirable hydrolysis of the ammonium salts formed, in the last stage. It is preferable to use the smallest practical amount of excess base in order to suppress emulsification as completely as possible and it may even be advantageous to employ amounts in the later extraction stage or stages which are too small to completely eliminate hydrolysis of the fatty acid salts. For although the distribution of free fatty acid between the solvent and oil phases is usually much less favorable than that of the corresponding salt, nevertheless, the oil can be sufficiently deacidifiedv by slightly increasing the number of extraction stages if difficulties from. emulsification are avoided. The amount of ammonia fed into the last extraction stage must, however, not be so small that the hydrolysis of the ammonium salts increases too much because in that case it would be necessary to use an unreasonably large number of extraction stages in order to obtain a product of specification free acid content. The best proportion to add in the later stage or stages in any particular case can be determined by simple experimental test but generally between about 5% and 50% or preferably between and 40% of the amount added in the first stage has been found to give good results.

The treatment is preferably carried out at ordinary temperatures or in the case of normally solid or highly viscous liquid starting materials at the lowest elevated temperature which will insure proper contact between the phases in-- volved. It may, however, be desirable to use higher or lower temperatures in certain cases particularly where more favorable distribution of the material or materials being extracted may be obtained thereby. When ammonia or like bases are used it is desirable to maintain temperatures below those at which amidization takes place in all stages of the treatment. Depending upon the nature of the solvent and temperature employed, it may be advantageous to use superatmospheric pressures but ordinary pressure can generally be employed. Batch or intermittent methods of operation may be employed although continuous procedures are preferred.

The following examples illustrate suitable methods for carrying out the invention and show some of the advantages obtainable thereby.

Example I 100 parts by volume palm oil, containing 6% fourth stage the refined on with a fatty acid content of 0.06% by weight was drawn oil, with a yield of 89% by weight after removal of solvent by vacuum distillation (maximum bath temperature 150 C.); from the first stage the extract was recovered and found after similar solvent removal and decomposition of the ammonium salt to contain 52% by weight free fatty acid. Similar results were obtained with ethyl alcohol.

No difilculties due to emulsification were experienced. On further reducing the amount of ammonia added in the fourth stage it was found that about one more extraction stage would be required to obtain a sufficiently deacidified palm oil railinate. In contrast these results may be compared with otherwise similar operations in which all the ammonium hydroxide was added in the fourth stage so that all conditions in the first stage and the ammonium salt concentration in all the. stages are precisely the same for both procedures, so that the only difference is that a much lower concentration of free ammonium hydroxide is present in stages 2, 3 and 4 of the first described process than in the corresponding stages of the procedure in which all the ammonia is introduced with the alcohol. Theoretically there is no reason to expect that a less stable emulsion would be formed in the first stage of one case than in the other but in practice it was found that less emulslfication took place in all stages of the procedure using split ammonia feed than when the ammonia was added only with the solvent. This appears to be probably due to the fact that no entrainment to the first stage occurs when the bulk of the ammonia is added in this stage because the other stages do not present anyemulsification difiiculties. On the other hand entrainment to stage one does occur when all the ammonia is added in the fourth stage since the emulsions in stages 2, 3 and 4 are difficult to completely separate in thiscase. As result of the higher ammonia concentrations present in r the later stagesand the long time of contact of by weight free fatty acid, were treated in countercurrent in 4 stages. each consisting of a mixer and a settler, with '75 parts by volume aqueous isopropyl alcohol (containing 15% by volume water), which was introduced in the fourth stage. In this stage 1.5 parts by volume ammonia of 10.4% concentration were also introduced, while 3.9 parts by volume ammonia of 10.4% concen tration were introduced in the first stage. The treatment was effected at 50 C. From the the esters with free ammonia resulting from the slowness of the breaking of the emulsions the loss of fat when the ammonia is all added in the last stage is much greater than when a part is added in the first stage.

Example I] I Acidity Color Percent Crude cocoanut oi1.. 6. 1 30y--5.3r Raflinate 0. 02 20y-2.6r Bleached product O. 02 5y0.8r

Cottonseed and soya bean oil were also refined with similar success although it was found to be advantageous in the case of the former to supplement the ammoniacal alcohol treatment with a final weak caustic soda wash in order to reduce the color.

Example III In order to show the effect of concentration of base upon the emulsiflcation tendencies of fatty oils a series of tests were made. At 60 C. 75 cubic centimeters of aqueous isopropyl alcohol was mixed with 100 cubic centimeters of Settling time Quantity of ammonia in minutes Also in the case of substantially completely deacidified palm oil (free acid 0.l% by weight) the time of settling was found to increase as larger quantities of ammonium hydroxide were added in spite of the substantial absence of ammonium salts-of fatty acids.

It is thus evident that the ammonium hydroxide itself gives rise to the formation of refractory emulsions. It is therefore important that the concentration of free base be kept as low as possible everywhere in the extraction system.

It will be seen that the process of the invention offers many advantages, particularly in efliciency and completeness of removal of impurities from ester type oils, fats and waxes with minimum loss of valuable components. Although the process has particular advantage in refining with ammonia and like volatile bases, particularly organic nitrogen bases such, for example, as are described in United States Patents 1,885,859 and 2,126,334, however, the invention is not limited to such basic agents but may also be applied with advantage to methods of refining in which sodium hydroxide, sodium carbonate, calcium oxide or other suitable alkali or alkaline earth metal or other suitable basic refining agents are employed. Mixtures of such bases may be used and/or the refining may be carried out successively with different bases.

Other suitable solvents which may be used instead of the ethyl and isopropyl alcohols described in the examples include, for example, methyl, tertiary butyl, allyl and like alcohols, or ketones such as acetone and methyl ethyl ketone or esters such as glycol mono-acetate or like water soluble solvents for the fatty acid salt involved which are incompletely miscible under the extraction conditions with the ester or ester mixture being refined.

The invention is applicable to the refining of fatty matter of widely different sources. Thus, for example, hot pressed, cold pressed and unclarified hot pressed California cottonseed oil, 7

soya bean oil, linseed oil, sardine oil, perilla oil, corn oil, peanut oil, cohune nut oil, and sundried and smoke dried copra oils, olive oil, etc. or fish oils such as cod liver oil, neats-foot oil, train oil,

sardine oil, cocoa butter, tallow, and the like may be advantageously refined.

It will thus be evident that the invention is capable of wide variation not only with respect to the starting materials which may be used but also with respect to the operating conditions which may be employed. Furthermore, the refining procedure may also difler from that described by way of illustration without departing from the invention thus, for example, it may be desirable to operate with a backwash treating stage as described inU. S. Patent 2,081,719 in order to increase the free fatty acid content of the extract although as will be seen from Example I the extracts obtained by the process of the invention even without backwashing are higher in free fatty acid than is the case of the usual aqueous caustic refining procedures which give extracts of about 35 to by weight. By reducing the extraction temperature to 40 C. in the process of Example I the content of free fatty acids in the extract may be raised by from 5 to 10% by weight. Another suitable method for increasing the free fatty acid content of the extract is to add an extraction section in which the extract phase is washed 'in countercurrent with a second solvent which is only partially miscible with the solvent used for the fatty oil extraction. Where initial solvents such as ethyl and isopropyl alcohol, etc. are used a hydrocarbon, .e. g. pentane, propane, gasoline fractions such as a to C. out of straight run or cracked gasoline or the like, may be employed. Since such hydrocarbons mix too well with aqueous ammoniacal isopropyl and ethyl alcohols of high concentration it is desirable to dilute the extract phase with water before subjecting it to hydrocarbon extraction. In this way a dilute alcohol solution containing soaps freed from fat may be obtained and a second (hydrocarbon) extract having the recovered fat. The latter may be recovered and returned to the crude oil feed by distilling off the hydrocarbon solvent which may be reused. The purified alcohol extract may also be distilled to separate alcohol, water and ammonia. The excess water used for dilution in the hydrocarbon extraction stage is preferably separated from the alcohol and returned to that stage and .not to the fatty oil extraction with the recovered alcohol otherwise settling difficulties in the latter may be encountered due to the density of the aqueous alcohol approaching too closely that of the fatty oil being refined. Still other variations may be made in theinvention which is not limited to the details disclosed nor by any theory suggested in explanation of the improved results obtained but only by the accompanying claims.

I claim as my invention:

1. In a process of refining an ester type oil comtaining free fatty acid by neutralization'of said acid with ammonia and multi-stage countercurrent extraction with aqueous isopropyl alcohol, the improvement which comprises introducing into the first extraction stage in which the oil is first contacted with said alcohol an amount of ammonia approximately equivalent stoichiometrically to the free acid content of said oil and into the last extraction stage from which refined oil is recovered an additional amount of ammonia between about 10% and 40% of the amount added in the first stage.

2. In a process of refining an ester type oil containing free fatty acid bycountercurrent extraction with an aqueous water soluble alcohol containing ammonia, the improvement which comprises introducing with the ester type oil an amount of ammonia approximately equivalent stoichiometrically to the free acid content of said oil, and adding with said solvent an amount containing free fatty acid by countercurrent extraction with an aqueous water soluble alcohol containing ammonia, the improvement which comprises introducing with the' ester type oil an amount of ammonia approximately equivalent stoichiometrically to the free acid content of said oil and adding with the alcohol feed an'additional amount of ammonia equivalent to between about 10% and 40% of that added with the oil.

4. In a process of refining an ester type oil containing free fatty acid by countercurrent ex- -20.

'taining free fatty acid by countercurrent extraction with an ammoniacal organic solvent for ammonium salts of said acid, the improvement which comprises introducing with the ester type oil an amount of ammonia approximately equivalent stoichiometrically to the free acid content of said oil and adding with the solvent feed an additional amount sufiicient to substantially suppress hydrolysis of ammonium salts of said fatty acid during at least the last stage of said extraction.

5. In a process of refining fatty matter containing free fatty acid by countercurrent extraction with an aqueous ammoniacal solvent for the ammonium salt of said acid, the improvement which comprises introducing with said fatty. matter an amount of base about equivalent to the free fatty acid content thereof and adding with said solvent substantially less ammonia than is stoichiometrically equivalent to the free fatty acid content of the crude fatty matter being treated but suflicient to at least partially suppress hydrolysis of salts of said fatty acid formed in the process.

6. In a process of refining fatty matter corrtaining-free fatty acid by countercurrent extraction with an aqueous ammoniacal organic solvent for-ammonium salts of said acid, the improvement which comprises introducing into the crude fatty matter feed end of the extraction system an amount of ammonia approximately stoichi-ometrically equivalent to the free fatty acid content of the fatty feed and adding with said solvent an amount of base sufficient to substan- 5 tially suppress hydrolysis of fatty acid salts formed in the process.

7. In a process of refining fatty matter containing free fatty acid by countercurrent extraction, in the presence of a base capable of forming a salt with said acid under the extraction conditions, with a solvent for said salt which is incompletely miscible with. the ester content of the fatty matter, the improvement which comprises introducing into the fatty matter feed end of the extraction system an amount of said base aboutstoichiometrically equivalent to the free 'fatty acid content of the crude fatty feed and into a later stage of the extraction between about 5% and of said amount of base.

8. In a process of refining fattymatter contraction, in the presence of a base capable of forming'a salt with said acid under the extraction conditions, with a solvent for said salt which is incompletely miscible with the ester content of the fatty matter, the improvement which comprises introducing into the fatty matter feed end of the extraction system an amount of said base about stoichiometrically equivalent to the free fatty acid content of the crude fatty feed and into the opposite end of the extraction systerm a lesser amount of said base sufficient toat least partially suppress hydrolysis of the salt of said fatty acid and base but insufficient to cause centration of free base sufficient to at least partially suppress hydrolysis of the formed salt of said fatty acid and base but insumcient to cause substantial emulsification.

WILLEM JOI-IANNES DOMINICUS VAN DIJCK. 

